For weeks, viewers (including yours truly) have wondered what’s up with Sam, who has not quite been acting right since he got back from the hellish prison he dove into at the end of last season … and mysteriously returned from at the beginning of this season. Last week, he even watched as Dean was turned into a vampire, apparently in an attempt to catch the Alpha Vampire.

Tonight’s episode starts with a waitress who gets a little too much truth. A customer, an old woman, offers that she once ran over a homeless man and didn’t even check to see if he’s okay. Her co-workers confide way too much information about what they think of her (of the not-positive variety). This all begins when she says, on the telephone, “I just need the truth. That’s all.” It ends with her blowing her own brains out.

Cut to Dean, who is on the phone with Bobby about how to find out the truth about Sam. I think you can see where this is heading.

They’ve tested him with everything – salt, holy water, silver, and so on – and there’s no indication that Sam is any kind of supernatural being that they’ve ever run into, so if he isn’t actually Sam, then what is he?

Meanwhile, the boys investigate a series of suicides, including the aforementioned waitress. When questioning the victim’s sister, Sam confronts her strongly on a bluff. Sam was always the sensitive one, but now he’s the intimidating one. He gets the woman to confess that she was on the phone with the sister and told her to just go ahead and kill herself, as if she couldn’t help herself.

Now the scene cuts to a dentist’s office and the man in the chair makes the mistake of saying, “I’ve got to be honest, Paul, I don’t really want to be here.” He then proceeds to talk about how he isn’t into his wife, “she’s old,” and instead he had an affair with the dentist’s daughter. The dentist, in a rage, attacks him with dental implements … one of the most disturbing scenes I’ve ever seen on the show.

Dean offers to do some research, which should trigger warning bells for Sam. He figures out that the dentist and one of the suicides both had a connection to the same music store. The store, as it turns out, has a stolen horn that went missing the same day as the first suicide. Dean figures that it may be Gabriel’s Horn of Truth … which is enough to get Castiel to show up, even though he’s been ignoring Dean’s pleas for information about Sam.

Castiel is able to tell Dean that Sam’s not Satan; he’d know if Lucifer had gotten out of the pit. After a quick check, he discovers that the Horn of Truth isn’t in town, but he does say that he’ll “make inquiries” into what’s up with Sam.

Sam’s investigation, meanwhile, turns up that the bodies of the victims related to the case are missing. Just gone, according to the coroner.

Dean, drinking in a bar, says, “I’d just like the freaking truth” … and we’re off to the races, as the bartender and a comely patron begin telling him personal details of their lives. After finding out too much information about Bobby’s taste in television (he’s a Tori Spelling fan) and personal grooming habits (he occasionally gets pedicures), Dean has a too-candid conversation with Lisa, which ends with him being told not to come back. Dean finally gets a chance to turn the inquisition onto Sam. Sam confesses that he froze in shock while Dean was attacked by the vampire (odd, because it certainly didn’t seem like he froze up).

The truth effect, it seems, is the result of the fact that a disgruntled girl with a cheating boyfriend summoned Veritas, the goddess of truth, to find out the truth. Veritas is now hanging around town granting requests for truth, then feasting on the victims … and if Dean isn’t careful, he’ll be the next victim. It turns out that Veritas needs to be worshiped for the mayhem she creates, which leads Dean to figure out that she’s a local news anchor who’s covering the stories.

Unfortunately, the attempt to catch her doesn’t go well and they get busted. She forces them into a game of “Truth or Truth,” in which Dean confesses that he is a killer. It’s what he’s good at and, though he wanted to do the family thing, he was never really suited to it. He’s a hunter.

When Veritas turns the game onto Sam, though, she’s in for a surprise: Sam can lie. “What are you? … You’re not human.”

Sam, however, has been cutting through the ropes binding him this whole time, so he takes the distraction of Veritas’ shock to attack her, sliding the knife over to Dean. They’re able to kill her, but then Dean turns the knife onto Sam.

Sam admits that something is wrong with him, but he doesn’t know what. He doesn’t care about the consequences of his actions. He doesn’t care that people could get hurt. In other words, Sam is now a sociopath. He feels no emotions and it makes him a better hunter than ever before.

So Dean beats him unconscious.

Fade to black.

And, according to the trailer, next week Castiel discovers that Sam has no soul in his body … which actually explains quite a lot about his recent behavior.